function calculateMortgage() {
// 1. Get Input Values
var homePrice = parseFloat(document.getElementById("homePrice").value) || 0;
var downPayment = parseFloat(document.getElementById("downPayment").value) || 0;
var loanTermYears = parseInt(document.getElementById("loanTerm").value) || 30;
var annualRate = parseFloat(document.getElementById("interestRate").value) || 0;
var yearlyTax = parseFloat(document.getElementById("propertyTax").value) || 0;
var yearlyIns = parseFloat(document.getElementById("homeInsurance").value) || 0;
var monthlyHOA = parseFloat(document.getElementById("hoaFees").value) || 0;
// 2. Validate basics
if (homePrice < 0 || downPayment 0) {
monthlyPrincipalInterest = principal / numberOfPayments;
} else {
monthlyPrincipalInterest = 0;
}
} else {
// Standard Mortgage Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var x = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPrincipalInterest = (principal * x * monthlyRate) / (x – 1);
}
var monthlyTax = yearlyTax / 12;
var monthlyIns = yearlyIns / 12;
var totalMonthlyPayment = monthlyPrincipalInterest + monthlyTax + monthlyIns + monthlyHOA;
var totalRepayment = (monthlyPrincipalInterest * numberOfPayments);
var totalInterest = totalRepayment – principal;
// 4. Update UI
// Helper for currency formatting
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById("resPrincipal").innerText = formatter.format(monthlyPrincipalInterest);
document.getElementById("resTax").innerText = formatter.format(monthlyTax);
document.getElementById("resIns").innerText = formatter.format(monthlyIns);
document.getElementById("resHOA").innerText = formatter.format(monthlyHOA);
document.getElementById("resTotal").innerText = formatter.format(totalMonthlyPayment);
document.getElementById("resLoanAmount").innerText = formatter.format(principal);
// Handle negative interest logic visual fix if bad input, though calculation handles math
if(totalInterest < 0) totalInterest = 0;
document.getElementById("resTotalInterest").innerText = formatter.format(totalInterest);
// Show results
document.getElementById("results").style.display = "block";
}
Understanding Your Mortgage Calculation
Buying a home is one of the most significant financial decisions you will make. This Mortgage Payment Calculator is designed to provide clarity on exactly what your monthly obligations will look like. Unlike basic calculators that only show Principal and Interest, this tool factors in the crucial "hidden" costs of homeownership: property taxes, homeowners insurance, and HOA fees.
The Components of Your Monthly Payment (PITI)
Lenders often refer to your payment as PITI. Here is what that means for your budget:
Principal: The portion of your payment that goes directly toward paying down the loan balance ($350,000 in our default example).
Interest: The cost of borrowing money. In the early years of a mortgage, a higher percentage of your payment goes toward interest rather than principal.
Taxes: Property taxes are usually collected by your lender and held in an escrow account to be paid to your local government annually.
Insurance: Homeowners insurance protects your property against damage. Like taxes, this is often bundled into your monthly payment via escrow.
How Interest Rates Affect Your Buying Power
Even a small difference in interest rates can have a massive impact on your monthly payment and the total cost of the loan. For example, on a $300,000 loan, the difference between a 6% and a 7% interest rate is roughly $200 per month. Over the life of a 30-year loan, that 1% difference costs you an extra $72,000.
Tips for Lowering Your Monthly Payment
If the calculated total is higher than your budget allows, consider these strategies:
Increase Your Down Payment: Putting 20% down avoids Private Mortgage Insurance (PMI) and lowers the principal amount.
Extend the Loan Term: Moving from a 15-year to a 30-year term lowers monthly payments, though you will pay more interest in the long run.
Shop for Insurance: Homeowners insurance rates vary significantly by provider. Shop around to find the best rate for your coverage needs.
Frequently Asked Questions
Does this calculator include PMI?
This specific calculator focuses on PITI and HOA. If your down payment is less than 20%, lenders typically require Private Mortgage Insurance (PMI), which generally costs between 0.5% and 1% of the entire loan amount annually.
What are HOA fees?
Homeowners Association (HOA) fees are payments made to an organization that manages a shared housing community. These are common in condos and planned neighborhoods and are paid in addition to your mortgage.